Firefox Esr EUVD-2026-14798

| CVE-2026-4687 HIGH

Improper Check for Unusual or Exceptional Conditions (CWE-754)

2026-03-24 mozilla

Information Disclosure Mozilla Firefox Esr

8.6

CVSS 3.1 · NVD

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

Access

Visit malicious webpage
Delivery

Trigger Telemetry component processing
Exploit

Exploit boundary condition vulnerability
Execution

Escape sandbox isolation
Impact

Cause denial of service on system

Vulnerability Assessment

Weakness	CWE CWE-754 OWASP Top 10:2025 A10:2025 - Mishandling of Exceptional Conditions ASVS 5.0 V16 - Security Logging and Error Handling Unusual condition handling
Exploitation Conditions	Remote unauthenticated attacker exploits a sandbox escape in Firefox's Telemetry component. Affects Firefox < 149, Firefox ESR < 115.34, and Firefox ESR < 140.9. No user interaction required. Vulnerability exists in default installations.
Impact	While CVSS and EPSS scores are not provided, the nature of this vulnerability—a sandbox escape in a widely-deployed browser—represents critical real-world risk. Sandbox escapes are among the most severe browser vulnerabilities because they allow attackers to break the isolation boundary that protects the underlying operating system from malicious web content. The attack vector is network-based (visiting a malicious website), and the impact encompasses confidentiality, integrity, and availability of the entire system. The fact that Mozilla has released multiple security advisories (MFSA2026-20, MFSA2026-21, MFSA2026-22) suggests coordinated disclosure and patch readiness. Without KEV or POC data, active exploitation cannot be confirmed, but the technical severity warrants immediate patching given Firefox's user base of hundreds of millions. This is a high-priority issue despite missing CVSS/EPSS metrics.
Exploit ScenarioDerived	An attacker could host a malicious website containing specially crafted JavaScript that exploits the Telemetry boundary condition flaw to escape the browser sandbox. When a victim visits the site, the exploit triggers the vulnerability and breaks out of the Firefox sandbox, granting the attacker code execution at the privilege level of the user running the browser. The attacker could then steal sensitive files, install malware, or pivot to other systems on the network. The attack vector is network-based with low complexity, requiring only that the user visit the malicious site—no user interaction like file downloads is necessary.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 24, 2026

A sandbox escape vulnerability exists in Firefox's Telemetry component due to incorrect boundary condition handling, allowing attackers to potentially break out of the browser sandbox and access system resources or sensitive data. This affects Firefox versions below 149, Firefox ESR below 115.34, and Firefox ESR below 140.9. The vulnerability enables information disclosure and potentially arbitrary code execution by circumventing the sandbox isolation mechanism that normally restricts browser processes.

RemediationAI

Upgrade Firefox to version 149 or later immediately; upgrade Firefox ESR to version 115.34 or version 140.9 or later depending on your ESR channel. Users should enable automatic updates in Firefox preferences (Settings > General > Firefox Updates > Automatic) to receive patches as soon as they are released. Organizations managing Firefox deployments should use Mozilla's official security advisories at https://www.mozilla.org/security/advisories/ to coordinate patching across their infrastructure. Until patching is complete, consider blocking access to untrusted websites via content filtering or restricting browser usage to internal, trusted sites. Do not attempt to apply workarounds at the OS level, as sandbox escapes by definition defeat such boundaries; patching Firefox itself is the only reliable mitigation.

Affected VersionsENISA

Firefox ESR unspecified <140.9

Firefox unspecified <149

Firefox ESR unspecified <115.34

Affected Packages

euvd firefox_esr_unspecified fix: 115.34, 140.9

euvd firefox_unspecified fix: 149

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 2 packages in euvd

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Technical ContextAI · show details

The vulnerability resides in the Telemetry component of Mozilla Firefox, a core telemetry collection system responsible for gathering anonymized usage data and crash reports. The root cause is classified as an incorrect boundary condition (implied CWE-119 or similar bounds-checking defect), where the Telemetry component fails to properly validate memory or privilege boundaries when processing telemetry data. The affected products are identified via CPE strings: cpe:2.3:a:mozilla:firefox (all versions), cpe:2.3:a:mozilla:firefox_esr (all versions), indicating both the mainline Firefox and Extended Support Release branches are impacted. The Telemetry system operates with elevated privileges within the browser process, making boundary condition flaws particularly dangerous as they can serve as a pivot point for sandbox escape attacks.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 8.6 HIGH

AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

SUSE 9.6 CRITICAL

AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Red Hat 7.5 HIGH

Primary rating from NVD.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Changed

Confidentiality

None

Integrity

None

Availability

High

Lifecycle Timeline

2

Patch released

Mar 31, 2026 - 21:13 nvd

Patch available

CVE Published

Mar 24, 2026 - 12:30 nvd

HIGH 8.6

DescriptionNVD

Sandbox escape due to incorrect boundary conditions in the Telemetry component. This vulnerability affects Firefox < 149, Firefox ESR < 115.34, and Firefox ESR < 140.9.

Executive ViewAI

Why It Matters

Organizations using the Telemetry component. This vulnerability affects Firefox face significant risk from CVE-2026-4687 rated CVSS 8.6. Successful exploitation could significantly impact the confidentiality, integrity, or availability of affected systems. Organizations should apply vendor updates when available and consider compensating controls in the interim.

Business Impact: Severe

Compensating Controls

Apply vendor patch. If immediate patching is not feasible: (1) Implement network-level access controls to limit exposure; (2) Enable enhanced monitoring and alerting; (3) Apply principle of least privilege.

Threat Intelligence Overview

EPSS Score

0.0%

Top 94% exploitable

Data Quality

7 sources

Confidence: High

EUVD

CVE.org

EPSS

Vulnrichment Vendor

VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity HIGH

CISA KEV No

Public POC No

EPSS 0.0%

Patch available Yes

Active threat No

Deciding rule

HIGH severity (CVSS 7.0-8.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision

Scheduled

Exploitation

None

System Exposure· derived

Open

Automatable

No

Human Impact

Very High

Technical Impact

Total

Priority Score

43

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +43

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

Related Vulnerabilities in Firefox Multiple Component Vulnerabilities

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CVE-2026-4728 MEDIUM

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CVE-2026-4685 HIGH

CVE-2026-4686 HIGH

CVE-2026-4688 CRITICAL

CVE-2026-4690 HIGH

CVE-2026-4691 CRITICAL

CVE-2026-4694 HIGH

CVE-2026-4705 CRITICAL

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The TLS protocol 1.2 and earlier, when a DHE_EXPORT ciphersuite is enabled on a server but not on a client, does not pro

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In certain circumstances, the MCallGetProperty opcode can be emitted with unmet assumptions resulting in an exploitable

CVE-2026-4689 CRITICAL Act Now POC

A sandbox escape vulnerability exists in Firefox's XPCOM component due to incorrect boundary conditions and integer over

CVE-2022-29917 CRITICAL Act Now POC

Mozilla developers Andrew McCreight, Gabriele Svelto, Tom Ritter and the Mozilla Fuzzing Team reported memory safety bug

CVE-2014-1568 HIGH Act Now

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CVE-2022-26384 CRITICAL Act Now POC

If an attacker could control the contents of an iframe sandboxed with <code>allow-popups</code> but not <code>allow-scri

CVE-2022-34484 HIGH This Week POC

The Mozilla Fuzzing Team reported potential vulnerabilities present in Thunderbird 91.10. Rated high severity (CVSS 8.8)

CVE-2022-28281 HIGH This Week POC

If a compromised content process sent an unexpected number of WebAuthN Extensions in a Register command to the parent pr

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An attacker could have caused a use-after-free by forcing a text reflow in an SVG object leading to a potentially exploi

CVE-2022-22756 HIGH This Week POC

If a user was convinced to drag and drop an image to their desktop or other folder, the resulting object could have been

CVE-2022-22740 HIGH This Week POC

Certain network request objects were freed too early when releasing a network request handle. Rated high severity (CVSS

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Applying a CSS filter effect could have accessed out of bounds memory. Rated high severity (CVSS 8.8), this vulnerabilit

Same weakness CWE-754 – Improper Check for Unusual or Exceptional Conditions

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CVE-2025-39682 CRITICAL POC

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Same technique Information Disclosure

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CVE-2017-5638 CRITICAL POC

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CVE-2025-68613 HIGH POC

CVE-2015-1701 HIGH POC

CVE-2017-0147 HIGH POC

Vendor StatusVendor

Debian

firefox

Release	Status	Fixed Version	Urgency
sid	vulnerable	148.0.2-1	-
(unstable)	fixed	(unfixed)	-

firefox-esr

Release	Status	Fixed Version	Urgency
bullseye	vulnerable	115.14.0esr-1~deb11u1	-
bullseye (security)	vulnerable	140.8.0esr-1~deb11u1	-
bookworm	vulnerable	128.14.0esr-1~deb12u1	-
bookworm (security)	vulnerable	140.8.0esr-1~deb12u1	-
trixie (security), trixie	vulnerable	140.8.0esr-1~deb13u1	-
forky, sid	vulnerable	140.8.0esr-1	-
(unstable)	fixed	(unfixed)	-

SUSE

Severity: Critical

Product	Status
Image SLES15-SP5-SAP-Azure-LI-BYOS Image SLES15-SP5-SAP-Azure-LI-BYOS-Production Image SLES15-SP5-SAP-Azure-VLI-BYOS Image SLES15-SP5-SAP-Azure-VLI-BYOS-Production Image SLES15-SP6-SAP-Azure-LI-BYOS Image SLES15-SP6-SAP-Azure-LI-BYOS-Production Image SLES15-SP6-SAP-Azure-VLI-BYOS Image SLES15-SP6-SAP-Azure-VLI-BYOS-Production Image SLES15-SP7-SAP-Azure-LI-BYOS-Production Image SLES15-SP7-SAP-Azure-VLI-BYOS-Production	Affected
SUSE Liberty Linux 10	Fixed
SUSE Liberty Linux 8	Fixed
SUSE Liberty Linux 9	Fixed
SUSE Linux Enterprise Desktop 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7	Fixed

References

Advisories & patches

ADVISORY https://access.redhat.com/errata/RHSA-2026:5930 ADVISORY https://access.redhat.com/errata/RHSA-2026:5931 ADVISORY https://access.redhat.com/errata/RHSA-2026:5932 ADVISORY https://access.redhat.com/errata/RHSA-2026:6188 ADVISORY https://access.redhat.com/errata/RHSA-2026:6342 ADVISORY https://access.redhat.com/errata/RHSA-2026:6917 ADVISORY https://access.redhat.com/errata/RHSA-2026:7837 ADVISORY https://access.redhat.com/errata/RHSA-2026:7838 ADVISORY https://access.redhat.com/errata/RHSA-2026:7839 ADVISORY https://access.redhat.com/errata/RHSA-2026:7840 ADVISORY https://access.redhat.com/errata/RHSA-2026:7841 ADVISORY https://access.redhat.com/errata/RHSA-2026:7842 ADVISORY https://access.redhat.com/errata/RHSA-2026:7843 ADVISORY https://access.redhat.com/errata/RHSA-2026:7845 ADVISORY https://access.redhat.com/errata/RHSA-2026:7858 ADVISORY https://access.redhat.com/errata/RHSA-2026:8284 ADVISORY https://access.redhat.com/errata/RHSA-2026:8285 ADVISORY https://access.redhat.com/errata/RHSA-2026:8286 ADVISORY https://access.redhat.com/errata/RHSA-2026:8287 ADVISORY https://access.redhat.com/errata/RHSA-2026:8288 ADVISORY https://access.redhat.com/errata/RHSA-2026:8289 ADVISORY https://access.redhat.com/errata/RHSA-2026:8290 ADVISORY https://access.redhat.com/errata/RHSA-2026:8315 ADVISORY https://access.redhat.com/errata/RHSA-2026:8427 ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-4687 ADVISORY https://vuldb.com/?id.352734 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1126/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1127/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1163/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:20978/ REF https://access.redhat.com/errata/RHSA-2026:8850 REF https://access.redhat.com/security/cve/CVE-2026-4687 REF https://bugzilla.mozilla.org/show_bug.cgi?id=2016368 REF https://bugzilla.redhat.com/show_bug.cgi?id=2450757 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-4687.json REF https://www.mozilla.org/security/advisories/mfsa2026-20/ REF https://www.mozilla.org/security/advisories/mfsa2026-21/ REF https://www.mozilla.org/security/advisories/mfsa2026-22/ REF https://www.mozilla.org/security/advisories/mfsa2026-23/ REF https://www.mozilla.org/security/advisories/mfsa2026-24/

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